While I guess anything's possible, it sews perfectly on my other machine, and on lighter bag leathers. I'll swap it out with something different first thing.
I think @wiz may be onto something with the timing. I've changed the timing twice since he posted and had worse results, and slightly better results. I'll try again tomorrow as my arthritis is telling me it's time to quit.
I also receive a new tensioner in the mail today, I'll put the timing back to where it was and try that tomorrow just to rule it out, then go back to the timing...will post back.